BACKGROUND: The aim of this study was to determine the hemodynamic and clinical changes after occlusion of polytetrafluoroethylene (PTFE) femorotibial grafts. METHODS: Twenty-seven patients were randomly selected from all patients who underwent femorotibial bypass grafting in our department. In 10 patients, the reversed autologous saphenous vein was used as graft, and in 17 patients a PTFE prosthesis was used. Out of the latter 17 patients, 10 began long-term aspirin therapy and 7 began oral anticoagulation with warfarin. RESULTS: Nine out of the 10 patients with occluded PTFE grafts and who received only aspirin therapy had a critical ischemia after occlusion of the graft, and 4 underwent major amputation. Among the 10 patients with occluded autologous vein bypass, critical ischemia was present in only 4 patients, and only 2 required some form of surgical therapy with no case of major amputation. CONCLUSIONS: After occlusion of a PTFE femorotibial graft, there is a condition of critical ischemia that is less common after occlusion of a vein graft. Oral anticoagulation seems to prevent these negative changes.